Sheet post-processing apparatus and sheet post-processing method

ABSTRACT

To provide a sheet post-processing apparatus for stapling and ejecting sheets conveyed from an image forming apparatus. The sheet post-processing apparatus comprises a processing tray to load the sheets conveyed from the image forming apparatus and a stapler to staple a sheet bundle of the sheets loaded on the processing tray, and the stapled sheet bundles are led to a sheet receiving tray and are ejected so that the stapling positions of the plurality of sheet bundles loaded on the sheet receiving tray are shifted from each other at each upper and lower stages.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2005-368279 filed on Dec. 21, 2005, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet post-processing apparatus and a sheet post-processing method for post-processing sheets ejected from an image forming apparatus such as a copier, a printer, or a composite device.

2. Description of the Related Art

In recent hears, in the image forming apparatus, to sort sheets after image forming or to perform a post process of sheets such as a stapling process, a sheet post-processing apparatus may be installed in the neighborhood of a sheet ejection section of the main body of the image forming apparatus. For example, the sheet post-processing apparatus for performing the stapling process aligns and staples a plurality of sheets (sheet bundles) by an aligning means, ejects the stapled sheet bundles to a sheet receiving tray, and stacks sequentially these sheet bundles on the sheet receiving tray.

For example, in U.S. Pat. No. 5,263,697, a stapling structure including a binding means for binding recording sheets ejected from the image forming apparatus, a moving means for moving the binding means along a plurality of binding positions of recording sheets, and a position control means for controlling the position of the moving means so as to make the final binding position of the present recording sheets coincide with the starting binding position of the next recording sheets is disclosed.

In the stapling structure disclosed in U.S. Pat. No. 5,263,697, the movement distance and movement time of the binding means can be reduced, though stapled recording sheets, when sequentially ejected, are ejected in the state that the binding positions are overlaid each other, so that the recording sheets bulge when stacked on the sheet receiving tray, thus it is necessary to restrict the number of stacking sheets. Further, when the succeeding sheet bundle stapled is ejected, a problem arises that it presses out the sheet bundle erased already on the tray.

There is a conventional sheet post-processing apparatus available which can perform the stapling process. However, a problem arises that when recording sheets are ejected and stacked on the sheet receiving tray, the stapling positions are overlaid each other, thus the number of stacking sheets is limited and by the succeeding sheet bundle stapled, the sheet bundle on the sheet receiving tray is pressed out and broken.

SUMMARY

An aspect of the present invention is to provide a sheet post-processing apparatus and a sheet post-processing method for reducing breaking of the stack when ejecting stapled sheets.

An embodiment of the present invention provides a sheet post-processing apparatus for stapling and ejecting sheets conveyed from an image forming apparatus, comprising a processing tray to load the sheets conveyed from the image forming apparatus; stapling means for stapling a sheet bundle of the sheets loaded on the processing tray; and ejection means for leading the stapled sheet bundle to a sheet receiving tray and ejecting the same so as to shift the stapling positions of the plurality of sheet bundles loaded on the sheet receiving tray from each other at each upper and lower stages.

Furthermore, an embodiment of the present invention provides a sheet post-processing method for stapling and ejecting sheets conveyed from an image forming apparatus, comprising loading the sheets conveyed from the image forming apparatus on a processing tray; stapling a sheet bundle of the sheets loaded on the processing tray by a stapler; and leading the stapled sheet bundles to the sheet receiving tray and ejecting the same so as to shift the stapling positions of the plurality of sheet bundles loaded on the sheet receiving tray from each other at each upper and lower stages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the essential section of the sheet post-processing apparatus relating to an embodiment of the present invention;

FIG. 2 is a top view showing the essential section of the sheet post-processing apparatus relating to the same embodiment;

FIG. 3 is a schematic block diagram showing the sheet post-processing apparatus relating to the same embodiment;

FIG. 4 is a perspective view showing the stapler of the sheet post-processing apparatus relating to the same embodiment;

FIG. 5 is a perspective view showing the longitudinal aligning roller of the sheet post-processing apparatus relating to the same embodiment;

FIG. 6 is an illustration showing the paddle of the sheet post-processing apparatus relating to the same embodiment;

FIG. 7 is a schematic perspective view showing the queuing tray and processing tray of the sheet post-processing apparatus relating to the same embodiment;

FIG. 8 is a top view showing the queuing tray and processing tray of the sheet post-processing apparatus relating to the same embodiment;

FIG. 9 is a schematic perspective view showing the transversal aligning plate and conveying belt of the sheet post-processing apparatus relating to the same embodiment;

FIG. 10 is an illustration showing the state that the sheet on the queuing tray or sheet receiving tray of the sheet post-processing apparatus relating to the same embodiment is pressed out;

FIG. 11 is an illustration showing the movement of the queuing tray of the sheet post-processing apparatus relating to the same embodiment is pressed out;

FIG. 12 is an illustration showing the operation after the stapling process by a general sheet post-processing apparatus;

FIG. 13 is an operation illustration for explaining the basic operation of the stapler of the sheet post-processing apparatus of the present invention;

FIGS. 14A to 14D are operation illustrations for explaining the stapling process and sheet ejection operation of the sheet post-processing apparatus of the present invention;

FIGS. 15A to 15C are operation illustrations for explaining the sheet ejection operation after the stapling process of the sheet post-processing apparatus of the present invention;

FIG. 16 is an operation illustration showing a modification in which the stapling positions of the sheet post-processing apparatus of the present invention are shifted alternately; and

FIGS. 17A and 17B are operation illustrations showing a modification in which the stapling positions of the sheet post-processing apparatus of the present invention are set at one position of the corner of each sheet bundle.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, an embodiment of the present invention will be explained in detail with reference to the accompanying drawings. Further, in the drawings, to the same parts, the same numerals are assigned and duplicated explanation will be omitted.

Embodiment 1

FIG. 1 is a perspective view showing the essential section of the sheet post-processing apparatus relating to an embodiment of the present invention, and FIG. 2 is a top view showing the essential section of the sheet post-processing apparatus relating to an embodiment of the present invention, and FIG. 3 is a drawing for explaining the schematic constitution of the sheet post-processing apparatus relating to an embodiment of the present invention. Further, FIGS. 4 to 11 are drawings for explaining the constitution of each unit of the sheet post-processing apparatus.

The concrete constitution and operation of each unit shown in FIGS. 1 and 2 will be made clear sequentially by the explanation of the drawings shown in FIG. 4 and subsequent figures. Firstly, the processing of sheets by the sheet post-processing apparatus of the present invention will be explained mainly by referring to FIG. 3.

Paper P on which an image is formed by image forming apparatus 5 such as a copier is ejected by a pair of exit rollers 6 and is conveyed by sheet post-processing apparatus 7. Sheet post-processing apparatus 7, as shown in FIG. 3, includes queuing tray 10, processing tray 12, stapler 14, first sheet receiving tray 16, second sheet receiving tray 18, fixed tray 19, and gate G.

Paper P ejected from pair of exit rollers 6 of image forming apparatus 5 is received by a pair of entrance rollers 22 installed in the neighborhood of the take-in port of sheet post-processing apparatus 7. Entrance rollers 22 are composed of entrance upper roller 22 a and entrance lower roller 22 b. Entrance rollers 22 are driven by motor for driving the entrance rollers 26 (FIG. 1).

On the downstream side of entrance rollers 22, gate G for branching sheets P received by entrance rollers 22 to two paths (flow paths) is installed. Gate G has a sectional shape of a wedge and the pointed part of the wedge is directed toward the neighborhood of the rolling surfaces of entrance rollers 22. Gate G is rotatably born by the side wall inside sheet post-processing apparatus 7. The pointed part of the wedge takes the first position pointing to entrance upper roller 22 a of entrance rollers 22 and the second position pointing to entrance lower roller 22 b thereof.

Namely, the first position is used to select the path when the post process is required for sheet P and the second position is used to select the path when the post process is not required for sheet P.

When gate G is at the first position, sheet P is fed to first sheet feed rollers 24 and is sent from first sheet feed rollers 24 to queuing tray 10. Between entrance rollers 22 and queuing tray 10, sheet path guide 36 (FIG. 1) for leading sheet P to first sheet feed rollers 24 is installed. First sheet feed rollers 24 are composed of an upper sheet feed roller and a lower sheet feed roller.

On the downstream side of queuing tray 10, processing tray 12 for stacking sheets P dropped and fed from queuing tray 10 is arranged. Processing tray 12, while sheets P are stapled by stapler 14 which is a processing mechanism for performing the post process, aligns and supports sheets P stacked.

When sheets of a predetermined number are accumulated on queuing tray 10, as shown in FIG. 7, tray members 10 a and 10 b are opened in the directions of arrows n and m by queuing tray motor 34 (FIG. 1) and sheets P are dropped onto processing tray 12 by the own weight and are fed to stapler 14.

Stapler 14, as shown in FIG. 4, is slidden and positioned by stapler driver 49 in direction u and performs the stapling process. Further, stapler 14 is composed of one unit and in FIG. 4, the conditions before and after sliding is shown. Processing tray 12, to align a plurality of sheets P dropped and fed from queuing tray 10 in the longitudinal direction which is the conveying direction, has a pair of upper longitudinal aligning roller 38 a and lower longitudinal aligning roller 38 b shown in FIGS. 5 and 6.

Upper and lower longitudinal aligning rollers 38 a and 38 b serve as bundle conveying rollers for grasping sheet bundle T after ending of the stapling process and taking out it from stapler 14. Upper longitudinal aligning roller 38 a is driven by motor for driving the upper longitudinal aligning roller 40 and lower longitudinal aligning roller 38 b is driven by motor for driving the lower longitudinal aligning roller 42.

Further, when sheet P is dropped and fed to processing tray 12, at the position where the rear end of sheet P is dropped, paddle 44 rotatable for aligning sheet P at the uppermost position loaded on processing tray 12 in the longitudinal direction is arranged.

Paddle 44, as shown in FIG. 6, includes receiving portion 44 a of sheets P dropped and fed to processing tray 12, slapping portion 44 b for slapping sheets P onto processing tray 12, and sending portion 44 c for aligning sheets P on processing tray 12 and is driven by paddle motor 46. Paddle 44 is made of a rubber material, thereby is elastic.

At the end of processing tray 12 on the side of stapler 14, stopper 45 for making contact with the rear end of sheet P and restricting the rear end position is installed. Almost at the center of processing tray 12, conveying belt 50 for conveying sheet bundle T which is stapled and is taken out from stapler 14 by upper and lower longitudinal aligning rollers 38 a and 38 b up to first sheet receiving tray 16 or second sheet receiving tray 18 is installed. To conveying belt 50, hook 50 a for hooking the rear end of sheet bundle T is attached.

Queuing tray 10 can drop and feed sheets P to processing tray 12, though it can be used to convey sheets P toward first sheet receiving tray 16 or second sheet receiving tray 18, and the conveyance of sheets P toward sheet receiving trays 16 and 18 is executed by bringing queuing tray roller 28 into contact with sheets P on queuing tray 10. Queuing tray roller 28 is controlled in the vertical movement by source for driving the queuing tray roller 30 and is driven to rotate by motor for driving the queuing tray roller (FIG. 2).

As shown in FIG. 3, queuing tray 10, to support sheets P so as to position the front end of each of sheets P higher than the rear end thereof, is arranged at an inclination angle of θ1. First sheet receiving tray 16 and second sheet receiving tray 18 are moved upward by receiving tray driver 52 and either of them is selected. First sheet receiving tray 16 or second sheet receiving tray 18 is moved upward or downward to an almost same height as that of queuing tray 10 or processing tray 12 when stacking sheets P to improve the alignment of sheets P to be ejected. Further, first sheet receiving tray 16 or second sheet receiving tray 18, to support sheets P so as to position the front end of each of sheets P higher than the rear end thereof, is arranged at an inclination angle of θ2.

As shown in FIGS. 7 and 8, queuing tray 10 has a pair of tray members 10 a and 10 b formed so that the wall surface thereof is projected, receives sheets P in the state that it slides in the width direction of sheets P, and supports both sides of sheets P. On tray members 10 a and 10 b , queuing stoppers 10 c and 10 d for controlling the rear ends of sheets P are installed.

Queuing tray 10 is slidden and moved by queuing tray motor 34 (FIG. 2). Between queuing tray 10 and processing tray 12, when dropping and feeding sheets P on queuing tray 10 to processing tray 12, to prevent sheets P from deviating from the conveying direction to the transverse direction perpendicular thereto and align sheets P in the transverse direction, as shown in FIG. 9, transversal aligning plates 47 a and 47 b are installed. Transversal aligning plates 47 a and 47 b can slide in direction v so as to fit to the width of sheets P by motor for moving the transversal aligning plate 48, thereby can change the aligning position.

As shown in FIG. 3, when gate G is at the second position, sheets P requiring no post process are fed to second sheet feed rollers 60 and furthermore, are fed to third sheet feed rollers 61. Second sheet feed rollers 60 and third sheet feed rollers 61 are respectively composed of an upper sheet feed roller and a lower sheet feed roller. Papers P conveyed from third sheet feed roller 61 are sent to fixed tray 19 installed on the top of sheet post-processing apparatus 7.

Further, by motors 26, 34, 40, 42, 46, and 48 for driving the various mechanisms aforementioned and drivers 49 and 52 are driven and controlled by a control circuit (not drawn).

Next, the operation of sheet post-processing apparatus 7 will be explained in accordance with the flow of sheets. When sheets P with an image formed by image forming apparatus 5 are fed from exit rollers 6, sheet post-processing apparatus 7, depending on (1) a case that sheets P are not post-processed, (2) a case that sheets P are post-processed and preceding sheet P finishes the post processing, and (3) a case that sheets P are post-processed and preceding sheet P is in execution of the post processing, performed different operations.

Firstly, in (1) the case of no execution of the post processing, the pointed part of the wedge of gate G is almost at the second position pointing to entrance lower roller 22 b. Papers P fed from entrance rollers 22 are fed to second sheet feed rollers 60 and furthermore are fed to third sheet feed rollers 61. Papers P fed from the third sheet feed rollers are ejected to fixed tray 19 on the top.

Next, (2) the case that the post process (the stapling process) is performed and there are no preceding sheets P on processing tray 12 will be described. At this time, queuing tray 10 slides and moves tray members 10 a and 10 b respectively up to the positions indicated by the dotted lines shown in FIG. 11 in the directions of arrows m and n to open the drop and feed path of sheets P. Further, transversal aligning plates 47 a and 47 b, to align sheets P dropped from sheet feed rollers 24 in the transverse direction, are arranged so as to make the interval between transversal aligning plates 47 a and 47 b almost equal to the width of sheets P. By doing this, sheets P fed by sheet feed rollers 24 are dropped and fed directly to processing tray 12 without interrupting the conveyance by queuing tray 10.

At time of drop and feed, upper longitudinal aligning roller 38 a is shifted upward and receiving portion 44 a of paddle 44 receives the rear ends of sheets P. Both sides of sheets P are dropped by keeping contact with transversal aligning plates 47 a and 47 b so as to align sheets P in the transverse direction. Next, paddle 44 rotates in the direction of arrow o shown in FIG. 6, and the rear ends of sheets P are dropped from receiving portion 44 a, and sheets P are slapped down on processing tray 12 by slapping portion 44 b.

Furthermore, paddle 44 sends sheets P in the direction of arrow q by sending portion 44 c, and the rear ends of sheets P make contact with stopper 45, and the alignment of sheets P in the longitudinal direction is completed. Further, the alignment of sheets P in the longitudinal direction on processing tray 12 may be executed by upper longitudinal aligning plate 38 a by moving it up and down each time.

By aligning sequentially sheets P with an image formed in the transverse direction and longitudinal direction in this way, sheets P are stacked from sheet feed rollers 24 directly on processing tray 12. When sheets P reach a predetermined number, stapler 14 staples sheets P on processing tray 12 at a desired position in a bundle shape and forms sheet bundle T. Hereafter, as shown in FIG. 6, upper longitudinal aligning roller 38 a rotating in the direction of arrow r and lower longitudinal aligning roller 38 b rotating in the direction of arrow s grasp sheet bundle T and convey it toward first sheet receiving tray 16.

The rear end of sheet bundle T, when passing through upper and lower longitudinal aligning rollers 38 a and 38 b, is hooked by hook 50 a of conveying belt 50 rotating in the direction of arrow t shown in FIG. 5 and is sent onto first sheet receiving tray 16.

Further, first sheet receiving tray 16 is arranged at an inclination angle of θ2 and the front end of each sheet is positioned higher than the rear end thereof, so that preceding sheet bundle T ejected on first sheet receiving tray 16 will not be pressed out by making contact with the front end of succeeding sheet bundle T. Further, even if preceding sheet bundle T is slightly shifted by succeeding sheets P, first sheet receiving tray has an inclination angle of θ2, so that sheet bundle T drops by its own weight and the stapling process of sheets P aligned and stacked in the state that the rear ends are aligned on first sheet receiving tray 16 is completed.

In this way, sheets are sequentially stacked on first sheet receiving tray 16. Further, first sheet receiving tray 16 is arranged at an inclination angle of θ2 and the front end of each sheet is positioned higher than the rear end thereof, so that for example, even if sheets P are ejected onto first sheet receiving tray 16 in the state that they are curled convexly, preceding sheets loaded on first sheet receiving tray 16 will not be pressed out by making contact with the front ends of succeeding sheets P. Namely, ejected sheets P are sequentially loaded on first sheet receiving tray 16 without disturbing the order.

Next, (3) the case that the stapling process is performed and preceding sheets P in execution of the stapling process remain on processing tray 12 will be described. At this time, queuing tray 10 slides and moves tray members 10 a and 10 b respectively from the positions indicated by the dotted lines shown in FIG. 11 in the opposite direction of the direction of arrow m and the opposite direction of the direction of arrow n and can support sheets P at the positions indicated by the solid lines shown in FIG. 11. Further, queuing tray roller 28 is shifted above queuing tray 10 so as to prevent sheets P from disturbance. Papers P ejected from image forming apparatus 5 and fed by sheet feed rollers 24 are loaded once on queuing tray 10 to wait for processing tray 12 to become empty.

Papers P loaded on queuing tray 10 are sent toward queuing stoppers 10 c and 10 d by queuing tray roller 28 which drops down onto queuing tray 10 and rotates in the opposite direction of the direction of arrow f shown in FIG. 3 and are longitudinally aligned by making the rear ends of sheets P touch queuing stoppers 10 c and 10 d. Furthermore, queuing tray 10 is arranged at an inclination angle of θ1 and the front end of each sheet is positioned higher than the rear end thereof, so that sheets P are aligned longitudinally by making the rear ends touch queuing stoppers 10 c and 10 d by the own weight.

Fed sheets P are sequentially loaded on queuing tray 10 without disturbing the order. Further, even if preceding sheets P are pressed and slightly shifted by succeeding sheets P, queuing tray 10 has an inclination angle of θ1, so that sheets P drop by the own weight down to the position where the rear ends make contact with queuing stoppers 10 c and 10 d and are aligned and stacked in the state that the rear ends are aligned on queuing tray 10.

During this period, when preceding sheets P on processing tray 12 are ejected on the side of first sheet receiving tray 16 and processing tray 12 becomes empty, queuing tray 10 slides and moves tray members 10 a and 10 b from the positions indicated by the solid lines shown in FIG. 11 via the positions indicated by the alternate long and short dash lines shown in FIG. 11 up to the positions indicated by the dotted lines shown in FIG. 11 respectively in the directions of arrows m and n.

By doing this, for example, two sheets P waiting on queuing tray 10, when tray members 10 a and 10 b reach the positions indicated by the alternate long and short dash lines shown in FIG. 11, are dropped and fed onto processing tray 12 from the interval between tray members 10 a and 10 b. At this time, transversal aligning plates 47 a and 47 b are arranged so that the interval therebetween becomes almost equal to the width of sheets P. Therefore, sheets P dropped from queuing tray 10 are controlled on both sides by transversal aligning plates 47 a and 47 b and are aligned in the transverse direction.

Lower side sheet P of two sheets P dropped from processing tray 12 is sent in the direction of arrow q by lower longitudinal aligning roller 38 b rotating in the opposite direction of the direction of arrow s shown in FIG. 6, and the rear end of sheet P makes contact with stopper 45, thus the alignment of sheets P in the longitudinal direction is completed. Upper side sheet P of two sheets P dropped from processing tray 12 is sent in the direction of arrow q by upper longitudinal aligning roller 38 a rotating in the opposite direction of the direction of arrow r, and the rear end of sheet P makes contact with stopper 45, thus the alignment of sheets P in the longitudinal direction is completed, and hereafter, upper longitudinal aligning roller 38 a is shifted upward.

Third and subsequent sheets P ejected from image forming apparatus 5 are dropped and fed directly to processing tray 12 from the interval between tray members 10 a and 10 b without waiting on queuing tray 10. Third and subsequent sheets P are sequentially aligned on sheets P which are previously loaded on processing tray 12 by paddle 44.

When sheets P loaded on processing tray 12 reach a predetermined number, sheets P are stapled by stapler 14 and sheet bundle T is formed. Hereafter, sheet bundle T is conveyed toward first sheet receiving tray 16 by upper and lower longitudinal aligning rollers 38 a and 38 b, and furthermore the rear end thereof is hooked by hook 50 a of conveying belt 50, and sheet bundle T is ejected onto first sheet receiving tray 16, and the stapling process of sheets P is completed.

The aforementioned is the explanation of the whole operation of sheet post-processing apparatus 7. Next, the constitution of the stapler and transversal aligner which are characteristic units of the present invention will be explained.

Generally, the stapling process includes binding of one corner of each sheet and binding of several places (for example, two places) along one edge of each sheet. Particularly in the case of binding several places, when a sheet bundle stapled is ejected, as shown in FIG. 12, sheet bundles T are stacked on sheet receiving tray 16, and stapling positions ST are overlaid each other and bulge, so that when succeeding sheet bundle T is ejected, sheet bundles T already ejected on tray 16 are pressed out and may be broken.

The sheet post-processing apparatus of the present invention is characteristic in that such bulging due to overlaid stapling positions is reduced and sheet bundles are prevented from breaking of the stack.

FIG. 13 is a drawing for explaining the operation of stapler 14. Stapler 14, as shown in FIG. 4, can slide in direction u by stapler driver 49 and when binding the corners of sheets P, it moves to the position indicated by the solid line or alternate long and short dash line shown in FIG. 13 and then performs the stapling process. Further, when binding several places (for example, two places) along the edges of sheets P, stapler 14 moves to the positions indicated by the dotted lines shown in FIG. 13 and performs stapling process ST.

FIGS. 14A to 14D are drawings for explaining the stapling method of the present invention, show the case of binding two places along the edge of sheet P, and explain the movement of stapler 14 and transversal aligning plates 47 a and 47 b.

FIG. 14A shows the state that sheet P is aligned at the normal aligning position by transversal aligning plates 47 a and 47 b. Transversal aligning plates 47 a and 47 b can move in the first direction (direction A1) perpendicular to the sheet conveying direction and the opposite direction (direction A2) of the first direction. In transversal aligning plate 47 a, position b1 is a specified position and in transversal aligning plate 47 b, position b2 is a specified position. When the transversal aligning plates are at the normal aligning positions, transversal aligning plates 47 a and 47 b move from positions b1 and b2 to positions c1 and c2 and sheets P are aligned in the width direction from both sides in the conveying direction.

On the other hand, stapler 14 is slidden in direction A1 along the edge of sheet P by stapler driver 49, is stopped at first stapling position al, and performs the stapling process. Next, stapler 14 is slidden in direction A1 by distance L1 along the edge of sheet P, is stopped at second stapling position a2, and performs the stapling process. In this way, stapler 14 is stopped at several places in the movement process and performs the stapling process.

When the stapling process at the first and second stapling positions is finished, as shown in FIG. 14B, transversal aligning plates 47 a and 47 b move in direction A2 at predetermined distance L2, and transversal aligning plate 47 a moves to position b1, and transversal aligning plate 47 b moves to specified position d2. By doing this, first sheet bundle T stapled is conveyed to the position shifted in direction A2 by distance L2 from the normal aligning position, and is conveyed to sheet receiving tray 16 (or 18) by conveying belt 50. Further, interval L1 between first stapling position a1 and second stapling position a2 is about 120 mm and ST indicates the stapled state.

When first sheet bundle T stapled in this way is ejected, transversal aligning plates 47 a and 47 b, as shown in FIG. 14C, move again to normal aligning positions c1 and c2, and sheets P conveyed next are aligned in the width direction by transversal aligning plates 47 a and 47 b after movement and aligned at this aligning position.

Stapler 14 is at previous second stapling position a2 and performs the stapling process at stapling position a2. Next, stapler 14 moves in direction A2 along the edge of sheet P by distance L1, is stopped at first stapling position a1, and performs the stapling process. In this way, stapler 14 stops at several places in the movement process in the opposite direction and performs the stapling process.

When the stapling process is finished in this way, as shown in FIG. 14D, transversal aligning plates 47 a and 47 b move in direction A1 at predetermined distance L2, and transversal aligning plate 47 a moves to specified position e1, and transversal aligning plate 47 b moves to position b2. By doing this, second sheet bundle T stapled is conveyed to the position shifted in direction A1 by distance L2 from the normal aligning position, and is conveyed to sheet receiving tray 16 (or 18) by conveying belt 50. And, the operations shown in FIGS. 14A to 14D are repeated and the stapling process is performed sequentially.

In the aforementioned movement of stapler 14, distance L1 between the first stapling position and the second stapling position depends on the binding intervals of sheets, while movement distance L2 of transversal aligning plates 47 a and 47 b in the separation direction from the normal aligning position may be a distance that stapling positions ST of the first sheet bundle and second sheet bundle which are stapled are not overlaid each other, for example, a distance that the stapling positions are shifted by about 15 mm. When movement distance L2 is set, for example, to less than L1/2, the movement distance of transversal aligning plates 47 a and 47 b can be made smaller.

As mentioned above, stapler 14, at the normal aligning position, can perform the stapling process during the alternating motion from position al to a2 and from position a2 to a1, thus the movement distance of stapler 14 can be minimized. Therefore, the time in correspondence with the movement of stapler 14 can be reduced and the process can be performed at high speed. Further, after the stapling process, transversal aligning plates 47 a and 47 b convey sheet bundles alternately in directions A1 and A2.

Further, in the examples shown in FIG. 14, the positions of transversal aligning plates 47 a and 47 b can be moved in directions A1 and A2 around the normal aligning positions, though the positions may be moved in either of directions A1 and A2.

Namely, the sheet bundle stapled in FIG. 14A is conveyed straight, and the sheet bundle conveyed next is stapled at the normal aligning position, and then transversal aligning plates 47 a and 47 b are moved in either of directions A1 and A2, and the concerned sheet bundle is shifted and conveyed from the sheet bundle conveyed previously. In this case, it is necessary to make the movement distance in one direction longer than distance L2, though the stapling positions of conveyed sheet bundles can be shifted from each other.

Further, in the example shown in FIG. 14, the first sheet bundle T subjected to a staple process is conveyed to the position shifted by the distance L2 in the direction A2 from the normal aligning position and conveyed to the sheet receiving tray 16 (or 18) by the conveying belt 50, and the next second sheet bundle T subjected to a staple process is conveyed to the position shifted by the distance L2 in the direction A1 from the normal aligning position and conveyed to the sheet receiving tray 16 (or 18) by the conveying belt 50. In other words, after the stapling process, the sheet bundles are shifted right and left and are conveyed to the sheet receiving tray. Alternatively, however, the sheet bundles may be shifted to the right and left, then stapled, and conveyed straight to the sheet receiving tray. That is, in the state shown in FIG. 14A, the first sheet bundle T is only aligned but not stapled and is shifted to the position shown in FIG. 14B in the direction A2. The first sheet bundle T so shifted is stapled, and then is conveyed onto the sheet receiving tray. Next, in the state shown in FIG. 14C, the second sheet bundle T is only aligned but not stapled and is shifted to the position shown in FIG. 14D in the direction A1. The second sheet bundle T shifted is stapled, and then is conveyed onto the sheet receiving tray.

FIGS. 15A to 15C show the situation that sheet bundles T stapled are sequentially ejected to sheet receiving tray 16, and FIG. 15A shows that stapling positions ST of sheet bundles T are shifted from each other at the upper and lower stages, and FIG. 15B shows the overlaying condition of stapling positions ST of sheet bundles T. As shown in FIG. 15B, the stapling positions are shifted from each other, thus height HI of the overlaid portion is lowered. Therefore, even if sheet bundles T are stacked on sheet receiving tray 16, the bulge can be lowered. Further, even if succeeding sheet bundle T is ejected, the phenomenon that sheet bundle T already ejected on tray 16 is pressed out can be reduced.

FIG. 15C shows the overlaying condition of sheet bundles T by the conventional stapling process for reference. In this case, the stapling positions are all the same position, so that height H2 of the overlaid portion is raised (H2>H1), thus the sheet bundles are broken.

As mentioned above, in the embodiment of the present invention, sheets stapled and ejected, when stacked on sheet receiving tray 16 (or 18), can be prevented from breaking and pressing out. Therefore, a sheet post-processing apparatus convenient to a user can be obtained free of a lowering of the efficiency of the image forming apparatus.

In the embodiment aforementioned, the stapling positions of every sheet bundle are the same positions, and the sheet bundles are shifted from each other after the stapling process and are ejected to sheet receiving tray 16 (or 18). However, the present invention is not limited to it.

As shown in FIG. 16, it is possible to shift alternately the stapling positions of sheet bundles T, staple them, and then eject them to sheet receiving tray 16 (or 18). Namely, first sheet bundle T1 is stapled at first stapling positions A1 and B1, and next second sheet bundle T2 is stapled at second stapling positions A2 and B2 shifted from first stapling positions A1 and B1, and next third sheet bundle T3 is stapled at first stapling positions A1 and B1 similarly to first sheet bundle T1, and next fourth sheet bundle T4 is stapled at second stapling positions A2 and B2 similarly to second sheet bundle T2. When sheet bundles T1, T2, T3, and T4 stapled in this way are ejected to sheet receiving tray 16 (or 18), as a result, as shown in FIG. 16, the sheet bundles are stacked on sheet receiving tray 16 (or 18) in the state that the stapling positions are shifted alternately. In this case, sheet bundles T1, T2, T3, and T4 are stacked on sheet receiving tray 16 (or 18) in the state that both sides thereof in the conveying direction are aligned.

Furthermore, as shown in FIG. 17A, when the stapling positions of sheet bundles T are set to one same place of the corners of sheet bundles T, similarly to FIG. 15B, after the stapling process, it is possible to shift alternately sheet bundles T and eject them to sheet receiving tray 16 (or 18).

Further, as shown in FIG. 17B, even when the stapling positions of sheet bundles T are set to one place of the corners of sheet bundles T, it is possible to shift alternately the stapling positions at one place of the corners of sheet bundles T, staple them, and then eject them to sheet receiving tray 16 (or 18). Namely, first sheet bundle T11 is stapled at first stapling position C1 of the corner thereof, and next second sheet bundle T12 is stapled at second stapling position C2 shifted from first stapling position C1, and next third sheet bundle T13 is stapled at first stapling position C1 similarly to first sheet bundle T11, and next fourth sheet bundle T14 is stapled at second stapling position C2 similarly to second sheet bundle T12. When sheet bundles T11, T12, T13, and T14 stapled in this way are ejected to sheet receiving tray 16 (or 18), as a result, as shown in FIG. 17B, the sheet bundles are stacked on sheet receiving tray 16 (or 18) in the state that the stapling positions are shifted alternately. In this case, sheet bundles T11, T12, T13, and T14 are stacked on sheet receiving tray 16 (or 18) in the state that both sides thereof in the conveying direction are aligned.

Further, the present invention is not limited to the above explanation and without being deviated from the claims, the present invention can be modified variously. For example, the examples that stapler 14 performs the stapling process at one place and two places are explained, though it can perform the stapling process at three places. 

1. A sheet post-processing apparatus for stapling and ejecting sheets conveyed from an image forming apparatus, comprising: processing tray means for loading the sheets conveyed from the image forming apparatus; stapling means for stapling a sheet bundle of the sheets loaded on the processing tray means; and ejection means for leading the stapled sheet bundle to a sheet receiving tray and ejecting the same so as to shift the stapling positions of the plurality of sheet bundles loaded on the sheet receiving tray from each other at each upper and lower stages.
 2. A sheet post-processing apparatus to staple and eject sheets conveyed from an image forming apparatus, comprising: a processing tray to load the sheets conveyed from the image forming apparatus; a stapler to staple a sheet bundle of the sheets loaded on the processing tray; and an ejection unit to leading the stapled sheet bundle to a sheet receiving tray and eject the same so as to shift the stapling positions of the sheet bundles loaded on the sheet receiving tray from each other at each upper and lower stages.
 3. The apparatus according to claim 2 further comprising: an aligning unit including a pair of aligning plates to align the sheets loaded on the processing tray from both sides in the conveying direction to move the pair of aligning plates to a normal aligning position and a position shifted from the normal aligning position by a predetermined distance in a direction perpendicular to the conveying direction, wherein the stapler can move along edges in the conveying direction of the sheets aligned by the aligning unit and staple the conveyed sheets at several places at the normal aligning position, and the sheet ejection unit leads the sheet bundles stapled onto the sheet receiving tray in the state that the sheet bundles are shifted from each other in the direction perpendicular to the conveying direction by the aligning unit.
 4. The apparatus according to claim 3, wherein: the aligning unit can move the pair of aligning plates to the normal aligning position and at a predetermined distance around the normal aligning position in a first direction perpendicular to the conveying direction and in a second direction opposite to the first direction, and the ejection unit leads the sheet bundles stapled at the normal aligning position onto the sheet receiving tray by shifting them alternately in the first direction and second direction.
 5. The apparatus according to claim 3, wherein: the stapler, when the pair of aligning plates are at the normal aligning position, moves in the first direction, and at a first position and a second position in the movement direction, staples sheets conveyed, and moves next the stapler in the opposite direction of the first direction and at the second position and first position in the movement direction, staples sheets conveyed next.
 6. The apparatus according to claim 3, wherein assuming an interval between stapling positions by the stapler as L1 and the predetermined distance of moving of the aligning unit from the normal aligning position as L2, L2<L1/2.
 7. The apparatus according to claim 3, wherein positions stapled by the stapler are at least two places along the edges of the sheets.
 8. The apparatus according to claim 3, wherein the aligning unit includes, in addition to the pair of aligning plates to align the sheets loaded on the processing tray from both sides in the conveying direction, second aligning unit to aligning the edges of the sheets in the conveying direction.
 9. The apparatus according to claim 8, wherein the second aligning unit includes a stopper installed on the stapler to stop the edges of the sheets in the conveying direction.
 10. The apparatus according to claim 2, wherein the stapler staples a first sheet bundle loaded on the processing tray at a first stapling position and staples a next second sheet bundle at a second stapling position shifted from the first stapling position, and the ejection unit ejects the first sheet bundle and second sheet bundle onto the sheet receiving tray.
 11. The apparatus according to claim 10, wherein the first sheet bundle and second sheet bundle are stacked on the sheet receiving tray in the state that both sides thereof in the conveying direction are aligned.
 12. The apparatus according to claim 10, wherein positions stapled by the stapler are at least two places along the edges of the sheets.
 13. The apparatus according to claim 10, wherein a position stapled by the stapler is one place of a corner of each sheet.
 14. A sheet post-processing method for stapling and ejecting sheets conveyed from an image forming apparatus, comprising: loading the sheets conveyed from the image forming apparatus on a processing tray; stapling a sheet bundle of the sheets loaded on the processing tray by a stapler; and leading the stapled sheet bundles to the sheet receiving tray and ejecting the same so as to shift the stapling positions of the sheet bundles loaded on the sheet receiving tray from each other at each upper and lower stages.
 15. The sheet post-processing method according to claim 14 further comprising: aligning the sheets loaded on the processing tray from both sides in the conveying direction by a pair of aligning plates, wherein the pair of aligning plates moves to a normal aligning position and a position shifted from the normal aligning position by a predetermined distance in a direction perpendicular to the conveying direction; the stapler moves along edges in the conveying direction of the sheets aligned and staples every conveyed sheet at several places at the normal aligning position; and the sheet bundles stapled are led onto the sheet receiving tray in the state that they are shifted from each other in the direction perpendicular to the conveying direction.
 16. The sheet post-processing method according to claim 15, wherein the pair of aligning plates are moved to the normal aligning position and at a predetermined distance around the normal aligning position in a first direction perpendicular to the conveying direction and in a second direction opposite to the first direction, and the sheet bundles stapled are moved onto the sheet receiving tray in the state that they are alternately shifted in the first direction and second direction.
 17. The sheet post-processing method according to claim 15, wherein when the pair of aligning plates are at the normal aligning position, the stapler moves in the first direction and at a first position and a second position in the movement direction, staples sheets conveyed, and the stapler moves next in the opposite direction of the first direction and at the second position and first position in the movement direction, staples sheets conveyed next.
 18. The sheet post-processing method according to claim 15, wherein assuming an interval between stapling positions by the stapler as L1 and the predetermined distance of moving from the normal aligning position as L2, L2<L1/2.
 19. The sheet post-processing method according to claim 14, wherein the stapler performs the stapling process for a first sheet bundle loaded on the processing tray at a first stapling position and performs the stapling process for a next second sheet bundle at a second stapling position shifted from the first stapling position, and the first sheet bundle and second sheet bundle stapled are ejected onto the sheet receiving tray.
 20. The sheet post-processing method according to claim 19, wherein the first sheet bundle and second sheet bundle are stacked on the sheet receiving tray in the state that both sides thereof in the conveying direction are aligned. 